Retention of added copper by two soils as affected by organic matter, CaCO 3, and exchangeable ions

Abstract

The effects of addition and removal of organic matter and CaCO 3 and of saturating a loam and a loamy sand soil with hydrogen (HCl treated), with calcium and with sodium on the retention of added copper were studied. Removal of organic matter reduced the copper-retaining capacity in soils, while addition of 1 to 4% humic acid to H 2O 2-treated soils increased the retention. Soil organic matter had higher specific copper retaining as well as fixing capacity than the added humic acid. Humic acid fixed about 62 and 49% of the copper it retained, while soil organic matter fixed about 65 and 61% in the loam and loamy sand respectively, which could not be extracted with 0.1 N HCl. About 30% extra copper retained by the added humic acid was exchangeable. Saturating the soils with hydrogen (HCl treatment) decreased the retention of added copper considerably but addition of CaCO 3 up to 8% increased the retention by increasing the pH of the soil system. The CaCO 3 induced retention was lower than caused by humic acid additions. The specific copper retention by native CaCO 3 was slightly higher than that of added CaCO 3. However, other changes associated with the pre-treatment of the soil may have caused those differences in specif is copper retention. Although CaCO 3 had as high a copper fixing capacity as organic matter its contribution towards exchangeable copper was negligible. Calcium and sodium saturation of hydrogen-saturated soils did increase the retention but could not attain the level of the original soil. Calcium favoured the retention more than sodium. The results, however, are confounded by changes in pH and possibly in the sesquioxides that accompanied these treatments. Fine-textured soils had higher retention capacity than coarse, textured soil. Washing with HCl and treating with H 2O 2 reduced, by about 43%, the copper retained by each of the soils studied.